1. Field of the Invention
The present invention relates to a liquid crystal display displaying images by utilizing a light source arranged behind a liquid crystal panel.
2. Description of the Related Art
In these years, the cathode ray tube (CRT), which has been traditionally a mainstream of displays has been replaced by the liquid crystal display, since the liquid crystal display has advantages such as low power consumption, space-saving feature, and low cost.
There are several types of liquid crystal displays when categorized by, for example, illumination methods in displaying images. As a representative example, a transmissive liquid crystal display, which displays images by utilizing a light source arranged behind a liquid crystal panel can be cited.
FIG. 1 shows a cross sectional structure of a traditional transmissive liquid crystal display. A liquid crystal display 91 mainly includes a liquid crystal panel 92, a luminaire 94 (so-called backlight) arranged behind the liquid crystal panel 92 (that is, opposite side of the observer side), and a diffusion sheet 931 arranged therebetween.
The liquid crystal panel 92 mainly includes a polarizing plate 920, a glass substrate 921, a color filter 922, a transparent electrode 923, an orientation film 924, a liquid crystal layer 925, an orientation film 926, a transparent pixel electrode 927, a glass substrate 928, and a polarizing plate 929 in this order from the observer side.
Here, in the color filter 922, color filters for respectively color-separating light emitted from the luminaire 94 into, for example, three primary colors of red (R), green (G), and blue (B) are arranged. FIG. 2 shows transmission characteristics of a general color filter. In FIG. 2, the horizontal axis represents wavelengths (nm) of incident light, and the vertical axis represents normalized transmittance. Reference symbols B9, G9, and R9 represent transmission characteristics of the color filter to blue light, green light, and red light, respectively.
For the luminaire 94, a cold-cathode fluorescent lamp 943 called CCFL is generally used as a light source. In addition, the luminaire 94 mainly includes a prism sheet 941, a diffusion sheet 942, a lamp reflector 944, a light guide plate 945, and a reflective sheet 946. FIG. 3 shows a light source spectrum of a general cold-cathode fluorescent lamp. In FIG. 3, the horizontal axis represents wavelengths (nm) of emitted light, and the vertical axis represents normalized spectral intensity. Reference symbols B10, G10, and R10 respectively represent peaks of blue light, green light, and red light. In addition, as a light source, a light emitting diode (LED) or the like may be used.
Here, light emitted from the cold-cathode fluorescent lamp 943 is reflected by the lamp reflector 944 and the reflective sheet 946, directed in the direction of the liquid crystal panel 92, spread over the whole area of the liquid crystal panel 92 by the light guide plate 945, evenly diffused by the diffusion sheets 942 and 931, oriented by the prism sheet 941, and emitted to the liquid crystal panel 92.
The light enters the liquid crystal panel 92, light with a light volume according to the voltage applied by an unshown driving circuit is transmitted to the observer side for every pixel. In general, the color filter having transmission characteristics as shown in FIG. 2 is used to perform color display.
For example, in Japanese Unexamined Patent Application Publication No. 2003-279988, a transmissive liquid crystal display capable of securing visibility to a certain degree even when used in the light environment by using a CCFL or an LED as a light source is disclosed.